This invention relates to fiber formed netting of an improved type and to composites formed therefrom. Fiber formed netting is the type of netting formed by means of an extrusion die which forms the individual strands or fibers of the net by extruding them from the die. The joints between strands, which form the strands into the net configuration, may be formed within the die or immediately after the strands exit the die. A variety of configurations are known such as square, diamond, twill, etc.
Composites making use of various types of netting including fiber formed (herein also termed extruded net) netting are generally known. In such composites the netting is laminated to one or more fabric overlays. Chief among such uses and composites are absorbent fabrics for disposable diapers, incontinent briefs, training pants, bandages, dressings, diaper holders and liners and feminine hygiene garments, medical gowns, medical drapes, mattress pads, blankets, sheets, clothing and the like. Since such garments desirably include elastic portions, it has been the practice to include in such composite articles a net which exhibits unidirectional stretch. Such a net typically includes elastic strands extending in one direction and non-elastic strands in another direction.
One such net is described in U.S. Pat. No. 6,391,420 B1, entitled BICOMPONENT ELASTOMERIC NETTING. In such net the different strands may have different composition and/or properties.
Another type of net is the so called Thermanet as described in U.S. Pat. Nos. 4,755,247; 4,661,389 and 4,410,587 in which a heat activated adhesive coating is provided on one or more strands of the netting for bonding the netting in a composite structure. This xe2x80x9ccoatingxe2x80x9d is coextruded simultaneously with the core netting.
The entire content of all the foregoing are incorporated herein by reference.
In general, this invention provides netting having some strands which are adhesive and some strands which have an elastic or other designed property. The strands may extend in different or in the same directions.
More particularly, this invention in one embodiment relates to a bicomponent netting that, in one direction features strands made with a polymer resin suitable for melting and adhesion in lamination to another substrate. The strands in the other direction may have any desirable feature, such as rigidity, strength, distinctive color, distinctive geometry, elasticity, etc. The preferred configuration in this embodiment of the invention is elasticity in the strands extending in the non-adhesive direction, but many other combinations are possible. Thus, an extruded, bicomponent netting of preferred form provides elastomeric properties in strands in one direction and an adhesive polymer in strands in the other direction as is more fully described below.
Netting is a convenient form for making a composite material in which elastomeric strands provide stretch and recovery properties in one direction and in which adhesive strands in another direction provide the bonding to the other material(s) forming the composite. Because of the bonding nature of the adhesive strands and the elastomeric nature of the elastomeric strands, the composite product retains most, if not all, of the netting""s elasticity, drape, breathability, moisture/fluid transfer capabilities, etc. It should be noted however, that the composite is elastic only if the component that the elastic netting is bonded to is elastic or deformable, or can be made so by post-treatment procedure.
One disadvantage with all previous netting products that do not feature a high degree of elasticity in one or both directions is that the non-elastic strands, when cut, have a stiff, sharp, somewhat abrasive, or xe2x80x9cpricklyxe2x80x9d edge. In applications where the netting composite is used in contact with human skin, these xe2x80x9cpricklyxe2x80x9d edges are irritating and unacceptable. The non-elastic strands are soft enough only when made from a material with a low enough modulus and low resin hardness. The low modulus required is typically only found in highly elastic, soft elastomer resins (resins similar to those used in elastic strands). However, one can not use the same or similar resins for the strands in both directions if one wants one set of strands to melt and bond to a fabric, as in the present invention, while the other set of strands remain virtually unaffected. The non-elastic strands must have a significantly lower melt temperature. Non-elastic strands also have other advantages beneficial to the making of the total product, such as improved web handling characteristics and non-blocking properties and generally lower raw material cost. Strands with such characteristics are described below.
For the adhesive strands to achieve a good mechanical bond to a fabric in lamination in order to form a composite structure, they must have certain minimum flow properties under pressure. The adhesive strands"" viscosity must be reduced to the point where it, under pressure, is fluid enough to at least partially be able to penetrate the fabric to which it is being laminated. As the adhesive resin""s viscosity is a function of its temperature, the minimum required flow properties can be characterized by temperature dependent material properties. For the current purpose, the adhesive resins"" softening temperature and melt temperature are suitable material properties. Many materials are somewhat conformable under pressure at their softening temperature, possibly capable of a weak mechanical bond if laminated at this temperature. At the material""s melt temperature, a much greater degree of molecular movement is possible, usually making the flow properties under pressure sufficient to form a mechanical bond to a fabric in lamination. The higher the temperature, the lower the adhesive resin""s viscosity, and the better the flow properties. Typically, one needs to laminate at a temperature above the adhesive resin""s melt temperature to achieve the desired bond to a fabric in lamination. In this application, the lamination temperature is generally somewhat higher than the adhesive resin""s melt temperature. However, in some instances, lamination temperatures as low as the adhesive resin""s softening temperature may be acceptably useful in forming a composite. Melt temperature is to be taken herein as referring to any acceptable temperature which functions to achieve bonding.
As already indicated, one major disadvantage of non-elastic strands is their xe2x80x9cpricklyxe2x80x9d ends. By melting and bonding the non-elastic adhesive strands into a fabric substrate, according to this invention, the non-elastic strand is flattened out, imbedded in the substrate, and is no longer a continuous structure, as the strand is partially disintegrated. All this contributes to reducing the intrinsic nature of the strand""s end to a point where it is no longer detectable by feel. However one can typically still visually see the remnants of the strand.
Also, the use of this type of netting in composites allows for more simple laminating operations and eliminates the need for additional adhesives. For example, this type of netting provides the opportunity to combine processes (extrusion with in-line lamination), and reduces the raw material cost by eliminating the need for powder or spray adhesives.